The chip type variable resistor which represents the variable electronic parts is, as conventionally well known, disclosed for example in the patent document 1.
The chip type variable resistor includes an insulating substrate formed in a chip type with a through hole provided at a central portion thereof, a resistance film provided on an upper surface thereof in an arcuate shape concentric with the through hole, an external terminal electrode corresponding to the respective end portions of the arcuate resistance film provided on the insulating substrate, and an internal terminal electrode plate made of a metal plate adhered to a lower-surface of the insulating substrate and including an integrally formed hollow shaft portion that fits in the through hole. On the upper surface side of the insulating substrate, an adjustment rotor formed of a metal plate in a bowl shape and including a sliding piece that makes contact with the resistance film, is fitted over an upper end portion of the shaft portion such that a bottom portion of the rotor makes close contact with the upper surface of the insulating substrate, and the rotor is rotatably mounted on the insulating substrate by crimping the upper end portion of the shaft portion to outwardly extend, thereby allowing insertion of a screwdriver into inside the rotor for rotating the rotor.
In the chip type variable resistor thus configured, the rotor that controls the resistance is designed to receive insertion of a screwdriver that rotates the rotor into an inner portion thereof. For the screwdriver to be sufficiently engaged with the rotor, a certain insertion depth for the screwdriver has to be secured inside the rotor.
In the conventional chip type variable resistor, however, the rotor is fitted over the upper end portion of the shaft portion such that the bottom portion of the rotor makes close contact with the upper surface of the insulating substrate, and the upper end portion of the shaft portion is crimped to outwardly extend over the bottom plate as described above, and therefore increasing the insertion depth of the screwdriver into an inner portion of the rotor leads to an increase in height of the rotor from the upper surface of the insulating substrate, and hence to an increase in overall height of the chip type variable resistor, thus incurring an increase in size of the chip type variable resistor.
However, reducing the thickness of the insulating substrate or forming a recess on the upper surface of the insulating substrate at a position where the bottom plate of the rotor is mounted in order to reduce the overall height leads to degradation in strength of the insulating substrate, thereby resulting in frequent cracking thereof, in the manufacturing process as well as in the implementation on a PCB.
Patent document 1: JP-A-H11-354307